Automotive impacts, whether incidental, accidental, or otherwise unintentional, are unfortunately all too commonplace. Impacts can occur at virtually any vehicle speed. Low speed impacts or contacts, common during parking activities, are often anticipated by an operator or driver and generally occur at such low speeds that safety measures, such as the deployment of air bags, are unnecessary. Higher speed impacts, such as those that occur at travel speeds, typically require safety measures, such as deployment of one or more airbags, to help protect the occupants of the vehicle. Understandably, the faster such impact events can be detected and confirmed at higher speed vehicle operation, the quicker safety measures can be deployed.
To this end, manufacturers determine the initiation of an impact event using an impact sensing system that includes one or more accelerometers located within the motor vehicle that communicate with a control module, e.g. airbag control module, that controls safety measure, e.g. airbag deployment. Each accelerometer senses changes in acceleration of the motor vehicle along its sensing axis. While such devices work well in some aspects, systems employing a single accelerometer within the crush zone have given way to more sophisticated detection arrangements that include more than one accelerometer sensor and which can employ multi-axis accelerometers to enhance the detection of offset impacts, or impacts occurring to a front corner of the motor vehicle or otherwise occurring off the axis of the accelerometer. Still other systems have improved upon these impact detection arrangements by increasing the number of accelerometers located within a frontal vehicle crush zone, or the forward bumper area of the motor vehicle. Although increasing the number of accelerometers has increased the responsiveness of the impact sensing system, these systems are not without their respective drawbacks.
Multiple accelerometer arrangements tend to be inconsistent between test crashes and are therefore difficult to calibrate. In addition, vehicle crush in the vicinity of an accelerometer during a crash can rotate the accelerometer such that its axis along which sensing is optimal is disposed at an angle relative to subsequently transmitted crushing force thereby reducing the accuracy of its signal output. Moreover, during a washout event, or an event during which the sensor system is subjected to non-impact vehicle suspension motion, such as driving over a pothole or the like, a delay of usually up to 15 milliseconds must be built into the system to determine if the system is detecting an impact event that would require deployment of a safety measure or whether a suspension-related impact, such as driving over a pothole or the like, has occurred. As a result, great efforts have been made to reduce the time needed to distinguish between major impact events that require deployment of safety measures and events more commonly associated with non-impact suspension motion or minor impact events that would not otherwise benefit from the deployment of a safety measure. FIGS. 7 and 8 graphically represent the detection signals associated with impact and non-impact events and evidence the difficulty associated with distinguishing impacts requiring safety measure deployment from inconsequential impacts.
As shown in FIG. 7, the impact sensing system of a vehicle traversing a rough road can generate an acceleration signal 20 that mimics the early stage acceleration signals 22 associated with a high-speed impact event. FIG. 8 similarly shows how an acceleration signal 24 produced during a low speed event, or an event where safety measures are unnecessary, can mimic an acceleration signal 26 produced during a high speed impact event, such as an offset or angular impact where deployment of safety measures would be desired. Notably, signals 24, 26 are nearly indistinguishable for the initial 0.05 seconds of the event. Understandably, the sooner the type of event can be accurately identified with confidence, the sooner safety measures can be deployed when necessary.
One attempt to provide a system that more readily distinguishes between types of impact events includes the system disclosed in applicants issued U.S. Pat. No. 7,207,410 titled “Apparatus and Method for Enhanced Impact Sensing”, the disclosure of which is incorporated herein. The impact sensing system disclosed therein includes at least one switch located at the tip of a frame rail in a vehicle crush zone that is associated with an acceleration sensor. The switch and sensor are operatively associated with a control module or controller to initiate safety measures upon confirmation of an impact event versus a non-impact event or an event otherwise not significant enough to require safety measure deployment. The controller alters a threshold associated with deployment of the safety measures in conjunction with assessment of a switch position to allow deployment of safety measures even though a threshold value associated with the accelerometer may not be satisfied. Although such a system provides a robust impact sensing and confirmation paradigm, it is desired to even further increase the expediency with which an impact can be detected and assessed for determining if a detected event requires deployment of safety measures, e.g. airbag deployment.
Therefore, there is a need for an automotive impact sensing system that can both quickly detect impacts and quickly differentiate between types of impact events.